A variety of cutting tools, handpieces, and contra-angle units have been devised for use in cutting a tooth in order to alleviate the discomfort, horror and pains experienced during a cutting operation. In addition, a variety of theoretical and technical developments have been made in respect of the anesthesia. Materials used for cutting tools changed from high speed tool steel to cemented carbide tool, whereby the useful life of the tools has been improved while simultaneously improving the sharpness of the cutting edge over a prolonged period of time. The shape accuracy of the cutting edge is made uniform, removing non-uniformity in the sharpness, which reduces a variation in the magnitude of force required for the cutting operation. The machining accuracy of various parts including the handpiece and contra-angle has also been improved. This resulted in an improvement in the accuracy of rotation of the rotating parts, minimizing a deflection of the rotating axis. Improvement in the machining and the assembling accuracy of ball bearings enables a high speed rotation on the order of 300,000 to 500,000 revolutions per minute. The development of a cutting tool utilizing diamond made it possible to reduce the cutting force required, as a result of a high speed cutting. An analysis of human engineering with respect to the unit construction covers a detailed examination of the workability, stability and the color which contributes to reducing the uneasiness, bringing forth a substantial improvement in the performance and the functionability.
Despite the various efforts made, there remains the discomfort, horror and pains experienced during the cutting of teeth. Since this is a mechanical cutting of teeth with a cutting tool, any effort to reduce the mechanical force required, to suppress dynamic behaviour of the teeth during the cutting operation and to eliminate dynamic stimulus factors applied to the nerves will be one way of alleviating the pains experienced. Therefore, the procedure to alleviate the pains will be (1) fixing the teeth, (2) reducing the cutting force required, and (3) the use of anesthesia. To fix the teeth, the bridge process which utilizes adjacent teeth is known. However, because a troublesome preparation is required to effect the bridge process, little use is made of this technique in practice. The step (2) can be challenged by utilizing a diamond tool having an improved sharpness. This brings forth a degree of desired effect in reducing the cutting force required, minimizing the dynamic bahavior of the teeth and alleviating the pains. However, a patient is still obliged to suffer the normal discomfort, horror and pains associated with tooth cutting. Consequently, when required, the step (3) is utilized by the injection of a narcotic or the use of laughing gas to remove pains. However, recently, the use of ordinary anesthesia is frequently forbidden for reasons of medicine shocks. If the use of anesthesia is permitted, an increased length of time is required for recovery. Hence, it will be seen that it will be desirable to achieve the cutting of teeth without suffering from the discomfort, horror and pains while avoiding the use of anesthesia.